Hot melt adhesives have found extensive use in industry in bonding, joining or fabrication of various structures, including construction of structures from synthetic polymeric films, such as polyethylene, polypropylene, etc.; foil, including metal foil such as aluminum foil, wax-coated or wax-impregnated cellulosic structures; and various non-woven materials whose constituents are based on polyolefins, polyesters, polyamides and acrylic-type polymers.
The modern trend in the packaging and disposable article industry, for example, is to use more of the plastic-based or plastic-finished constructions, such as polyethylene or polypropylene based extrusion coated, spray coated, or laminated composite constructions. The change in various packaging and disposable laminate from fibrous substrates, such as fabrics and paper or paperboard, to plastics based on synthetic polymers also necessitates that the various adhesives chosen to hold the structures together be compatible with the materials of construction, since the altered surface chemistry of such materials may not be adhesion compatible with traditionally-available hot melt adhesives.
Hot melt adhesives based on homopolymers or copolymers of 1-butene (hereinafter "poly-1-butenes") are commonly used to bond fabrics or non-woven sheets to other porous or semi-porous substrates. Poly-1-butenes' polymorphic nature and unique crystallization half-life allow adhesives based on this polymer to flow and remain tacky long after they have cooled to room temperature and thus have relatively long open time. As used herein, adhesion open time is the maximum time at which adhesion (adhesion to itself or to a substrate) can take place for material after it is cooled from the melt to room temperature. Consequently, poly-1-butene based hot melt adhesives can be easily applied to cold substrates and will cold flow into porous substrates before the material undergoes further transition and densification.
On smooth substrates such as olefinic films and metals especially painted metals and coated metals, the surface is much different from those with porous substrates. As a result, poly-1-butene based hot melt adhesives do not adequately wet the smooth surfaces and tend to pop off or delaminate after the phase transition.
Disposable articles such as baby diapers, adult incontinence briefs, sanitary napkins, etc. typically use adhesives between the outer spun-bonded non-woven fabric, often made of polyolefins such as polypropylene, and the adsorbent core. Adhesives are also used between the absorbent core and the polyolefin liquid barrier, typically a polyolefin film such as a polyethylene film. These adhesives typically have hot melt (350.degree. F.) viscosities of less than 10,000 cP and therefore can be applied by spray coating techniques.
Poly-1-butene adhesives have offered formulators unique opportunities in the market as the adhesive between the polypropylene fabric and the absorbent core.
However, poly-1-butene inherently does not adhere very well to smooth surfaces, which have less surface areas than fabrics, such as painted/coated metals and polyolefin films, especially those outer liquid barrier films made of polyolefins such as polyethylenes. Because of this, formulators and diaper manufacturers were not able to utilize poly-1-butene based adhesives to adhere outer liquid barrier films until Lakshmanan et al. (U.S. Pat. No. 4,833,192) added liquid polybutenes, copolymers of isobutylene and butenes, to poly-1-butene adhesives to enhance their adhesion to polyethylene film. The present invention provides poly-1-butene based hot melt adhesives with good adhesion to both polyolefin fabrics and smooth polyolefin films which are superior to those containing liquid polybutenes.